1. Field of the Invention
The present invention relates generally to equipment for cleaning steam generators, and particularly to an improved articulated fluid lance having an extension nozzle that is movable for bringing the fluid jet into close proximity with the broached holes in the support plates for a nuclear steam generator for more efficiently cleaning sludge from steam generators.
2. Description of the Related Art
In nuclear power stations, steam generators, such as recirculating steam generators and once-through steam generators, are used for heat exchange purposes in the generation of steam to drive the turbines. Primary fluid which is heated by the core of the nuclear reactor passes through a bundle of tubes in the steam generator. The secondary fluid, generally water, which is fed into the space surrounding the tubes receives heat from the tubes and is converted into steam for driving the turbines. After cooling and condensation has occurred, the secondary fluid is directed back into the space around the tubes to provide a continuous steam generation cycle. Due to the constant high temperature and severe operating conditions, sludge accumulates on the lower portions of the tubes, support plates, and on the tube sheet which supports same. The sludge which is mainly comprised of an iron oxide, such as magnetite, reduces the heat transfer efficiency of the tubes and can cause corrosion. Thus, the tubes must be cleaned periodically to remove the sludge and various types of apparatus and method are available to accomplish this task.
U.S. Pat. No. 4,980,120 which is assigned to the Assignee of the present invention, and hereby incorporated by reference, discloses an articulated sludge lance.
In addition, U.S. Pat. No. 4,980,120 in the background art section describes various other techniques found in U.S. Pat. Nos. 4,566,406; 4,079,701 and 4,700,662.
In addition to those references, U.S. Pat. No. 4,407,236 to Schukei, et al discloses a thin strip of spring steel which enters a tube lane for sludge lance cleaning for nuclear steam generators. The forward ends of the capillary tubes are directed downward for the jetting of fluid under high pressure.
U.S. Pat. No. 4,827,953 to Lee is directed to a flexible lance for steam generator secondary side sludge removal. This patent discloses a flexible lance having a plurality of hollow, flexible tubes extending lengthwise along the flexible member. There are a plurality of nozzles at an end of the flexible members with the flexible member being configured to go into the difficult to access geometry of the steam generator.
When using the articulated sludge lance, penetration into the steam generator must be at least seven inches below the individual support plates due to stress considerations. This means jetting water from seven inches away while moving the articulated sludge lance parallel to the support plate. It has been found that the effectiveness of the cleaning diminishes considerably with distance from the support plate. Of particular concern is the deposits blocking broached holes.
Because of the foregoing, it has become desirable to develop an improved articulated sludge lance which jets the fluid at close proximity to the broached support plate taking into consideration the stress factors.